Japanese laid-open Patent Publication No. 2002-156010 discloses a power tool having a safety clutch using a planetary gear mechanism. In this power tool, an outer ring member in the planetary gear mechanism is pressed and held by a contact element defined by a brake shoe. When a tool bit is unintentionally locked during drilling operation, the outer ring member held by the contact element is released, so that a torque reaction force no longer acts on a tool body and the tool body is prevented from being swung.
With the safety clutch using the planetary gear mechanism, however, size reduction of the power tool is difficult.